The invention relates to a welding carriage for welding two overlapping webs of material.
Welding carriages are generally known and are preferably used for welding plastic films overlapping in the transverse direction for sealing roofs. The known welding carriages, however, are not limited to this special application. They are additionally suitable, for example, for welding lorry tarpaulins, tents, covers used in agriculture, swimming pool covers, awnings, boat tarpaulins, advertising awnings, floor coverings, etc. The essential thing is that the webs of material to be welded be arranged in overlapping manner so that a welding nozzle of a welding device arranged on the welding carriage can be positioned between the webs of material in order to heat up the overlapping sections of material on traversal of the welding carriage and hence to weld them. In known welding carriages a pressing device is usually arranged behind the welding nozzle in the welding direction to apply pressure to the upper web of material after the welding operation so that the upper web of material has pressure applied to it after heating on traversal of the welding carriage as a result of which an intimate bond is produced between the slightly fused webs of material. Such a welding carriage is disclosed, for example, in EP 1 371 474 B1. A disadvantage of the known welding carriage is that it can be operated in only one welding direction (operating direction).
When welding overlapping webs of material the procedure for doing so must be as shown in FIG. 11. In FIG. 11 two overlapping sections A and B extending in the longitudinal direction and spaced apart from one another in the transverse direction are shown, wherein in the overlapping section A a first web of material a overlaps a neighbouring second parallel web of material b in the transverse direction and in the overlapping section B the second web of material b overlaps a neighbouring third parallel web of material c. At position I the welding nozzle of a welding carriage is first of all positioned in the overlapping section A between the webs of material a and b and after this displaced along the dotted line up to position II in a first longitudinal direction. In the traversal of the welding carriage from position I to position II the fused weld tracks are pressed against one another by a pressing device arranged behind the welding nozzle in the first direction of travel. At position II the welding nozzle is moved out of the overlapping section A and after this the entire welding carriage is transported counter to the first direction of travel (only possible operating direction) into a second direction of travel that is also transverse thereto along the dotted line from position II to position III, wherein during this transport operation no welding ensues. Position III is located spaced apart in the transverse direction from the starting position I. At position III the welding nozzle is positioned in the overlapping section B between the webs of material b and c and the welding carriage is displaced in the first longitudinal direction again along the dotted line in the direction of the arrow to position IV, wherein in doing so the webs of material b and c are welded to one another. For welding further parallel webs of material to one another the welding carriage must now be transported once again counter to the welding direction (first longitudinal direction) and transverse thereto. Due to the sometimes very long transport step (II-III), especially in the case of large roofs, after the welding of two webs of material a considerable proportion of the available working time is not productively utilised since while traversing the long transport pathway no welding work can be carried out.
Other examples of known welding carriages are described in CH 4,65197, DE 3537244 A1, DE 423088 C2, DE 9110487 U1, DE 9110488 U1, DE 100 32 450 A1, DE 198 136 25 C1, EP 300 209 A2, EP 949 057 B1, EP 1464471 B1, U.S. Pat. No. 3,080,910, U.S. Pat. No. 4,440,588 and U.S. Pat. No. 5,865,942.
It is an object of the invention to propose a welding carriage by means of which a plurality of overlapping webs of material arranged alongside one another can be effectively and rapidly welded to one another. Furthermore, a method is to be proposed by means of which the neighbouring webs of material can be welded to one another in the shortest time using a welding carriage.